Carbonium Ions: Structural and Energetic Investigations

Abstract

Of the many inroads made by ab initio molecular orbital theory in recent years, perhaps the most impressive have been efforts directed at questions of structure and stability of reactive chemical intermediates. Such species are generally too short-lived to be amenable to direct spectroscopic observation and characterization. Hence, even the most rudimentary knowledge about them— information that might normally be taken for granted—must be gained from theory and not by experimental probes. For example, a half-century of chemical intuition, resting primarily upon experiment, leads us to suggest a tetrahedral geometry for methane, but this chemical intuition has little to offer regarding possible structures which the molecule might adopt after being protonated. That is to say, there is no precedent in our accumulated experience for such a species, nor do we have the tools ready in our experimental arsenal to explore the issue.